Genetics

1. Genetics

2. Gregor Mendel - studied pea plants, looked at traits. • Heritable features (characters) with different variants (traits). • Pea plants self-fertilize; Mendel cross-fertilized to study traits.

4. Mendel cross-pollinated (hybridized) 2 true-breeding pea varieties. • True-breeding parents - P generation; hybrid offspring - F1 generation. • F1 hybrids then self-pollinate to produce F2 generation.

5. http://nitro.biosci.arizona.edu/courses/EEB320-2005/Lecture02/pics/pea.jpeghttp://nitro.biosci.arizona.edu/courses/EEB320-2005/Lecture02/pics/pea.jpeg

6. Thought genes blended - purple flower crossed with white flower result would be light purple flowers. • All the flowers purple.

8. F1 self-fertilized, white flower reappeared in next generation. • Ratio of purple to white in F2 generation was 3:1.

11. Mendel’s hypotheses: • 1Alternative versions of genes (alleles) account for variations. • 2Organism inherits 2 alleles, 1 from each parent - can be same or different.

13. 32 alleles differ - dominant allele fully expressed in organism. • Recessive - no noticeable effect on organism’s appearance. • 42 alleles segregate (separate) during gamete production.

14. http://discover.edventures.com/images/termlib/d/dominant_allele/support.gifhttp://discover.edventures.com/images/termlib/d/dominant_allele/support.gif

15. Mendel’s laws: • 1Dominance and recessiveness - one gene is dominant over the more recessive gene. • 2Segregation - alleles separate during meiosis. • 3Independent assortment - alleles organize in gametes regardless of other alleles.

16. http://www.switchbackfair.co.uk/encyclopedia/images/genetics_peas.pnghttp://www.switchbackfair.co.uk/encyclopedia/images/genetics_peas.png

17. Punnett square predicts results of genetic cross between individuals. • Testcross - breeding homozygous recessive with dominant phenotype but unknown genotype.

19. Started with monohybrid crosses meaning (one trait at a time) • Then did dihybrid crosses (two different traits)

20. Based on probability. • Toss coin 4 times - ½ chance - heads every time. • Tosses independent of each other. • Coming up heads all four times - ½ * ½ * ½ * ½ = 1/16 - rule of multiplication.

21. 12.2

22. Law of addition - chances of an event happening in different ways. • 2 ways F1 gametes can combine to form heterozygote; dominant allele from sperm, recessive from ovum (= 1/4). • Dominant allele from ovum, recessive from sperm (= 1/4). • Probability of heterozygote is 1/4 + 1/4 = 1/2.

23. Incomplete dominance - heterozygotes have completely different phenotype than homozygotes (can happen in snapdragons) • Homozygous recessive flowers - white; homozygous dominant - red; heterozygotes - pink.

25. Codominance - two alleles affect phenotype in separate, distinguishable ways (example blood type) • Inherit A allele and B allele - blood type will be AB; AA or AO - blood type will be A. • A is dominant to O, B is dominant to O, but A is codominant to B.

26. http://blogsci.com/images/ABO_blood_type.jpg

27. Type A - anti-B antibodies. • Exposed to B blood - clump together causing a transfusion reaction. • Type O - both antibodies - can donate to any other blood type. • AB - neither antibodies - can receive from any blood type.

29. Most genes do not control only one trait but are pleiotropic - affecting more than one phenotypic character. • Epistasis - gene at one locus alters phenotypic expression of gene at second locus.

30. http://courses.bio.psu.edu/fall2005/biol110/tutorials/tutorial5_files/figure_14_11.gifhttp://courses.bio.psu.edu/fall2005/biol110/tutorials/tutorial5_files/figure_14_11.gif

31. Example - In mice, one gene determines whether or not there will be coat color. • If gene is turned off, mouse will be white; if turned on, another locus will determine what color is (brown or black).

32. Quantitative characteristics vary along continuum - polygenic inheritance - more than one gene controls single trait. • Skin color controlled by at least three different genes - responsible for variety of skin colors.

34. Phenotype depends on environment. • Humans - nutrition influences height, exercise alters build, sun-tanning darkens skin, experience improves performance on intelligence tests.

35. Geneticists use pedigrees to look at traits found in families. • Family tree created showing absence or presence of specific trait to determine how it is passed.

37. Ethnicity plays role in genetic disease patterns. • Sickle-cell anemia found predominately in African-Americans. • Causes red blood cells to be sickle shaped instead of normal shape causing cells to get stuck in vessels.

39. Cystic fibrosis affects mostly Caucasians. • Cystic fibrosis - multi-system disease - causes mucous to build up in various organs, especially lungs.

40. Tay-Sachs affects people of Jewish descent. • Tay-Sachs affects brains of small children causing death of child prior to 5 years old.

41. Dominant Diseases • Dwarfism - child 50% chance of inheriting disease because one parents has it. • Huntington’s affects nervous system. • Most dominant diseases not lethal (Huntington’s disease is).

42. Genetic counseling works with people that have history of genetic disease in family. • Child with recessive disease can be born to phenotypically normal parents. • Tests are performed to determine couple’s risk.

43. 1Amniocentesis - cells extracted from amniotic fluid surrounding fetus; then analyzed to search for potential problems through karyotyping. • Karyotyping - mapping out chromosomes of individual.

45. * • 2Chorionic villus sampling (CVS) - faster karyotyping - extracts sample of fetal tissue from chorionic villi of placenta. • 3Ultrasound detects only physical abnormalities present.

47. http://www.bookwood.com/triplets/Images/12WEEKS_ALL3.JPG

48. Thomas Morgan - fruit fly eye color. • Wild type (normal) eye color - red; mutant - white. • Discovered mutant eye color appeared more often in males - some traits sex-linked (carried on sex chromosomes).

50. Chromosomes have hundreds or thousands of genes. • Genes located on same chromosome, linked genes, inherited together - chromosome passed as unit.